Respiratory mask having gas washout vent and method for making the mask

ABSTRACT

A washout vent for a mask for use with a system for supplying breathable gas pressurized above atmospheric pressure to an airway of a mammal. The washout vent includes a vent orifice adapted for gas washout. The orifice includes one or more features that contribute to noise reduction, such as a channel with converging walls towards atmosphere, and/or a channel having one or more walls provided with surface treatment and/or contouring, such as roughening and/or scalloped portions.

CROSS-REFERENCE TO APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/598,598, filed Jan. 16, 2015, which is a continuation of U.S. patentapplication Ser. No. 11/793,001, filed Mar. 17, 2010, now U.S. Pat. No.8,967,146, which is the U.S. National Phase of International PatentApplication No. PCT/AU2006/000036, filed Jan. 12, 2006, which claims thebenefit of U.S. Provisional Application No. 60/643,114, filed Jan. 12,2005, and 60/714,910, filed Sep. 8, 2005, each of which is incorporatedherein by reference in its entirety.

Also, U.S. Provisional Application No. 60/590,338, filed 23 Jul. 2004,by Fu and Saada, is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Treatment of sleep disordered breathing (SDB), such as obstructive sleepapnea (OSA), by continuous positive airway pressure (CPAP) flowgenerator systems involves the continuous delivery of air (or otherbreathable gas) pressurized above atmospheric pressure to the airways ofa human or other mammalian patient via a conduit and a mask. Typically,the mask fits over the mouth and/or nose of the patient. Pressurized airflows to the mask and to the airways of the patient via the nose and/ormouth. As the patient exhales, carbon dioxide gas may collect in themask. A washout vent in the mask or conduit discharges the exhaled gasfrom the mask atmosphere.

The washout vent is normally located in the mask or near the mask in thegas delivery conduit coupled to the mask. The washout of gas through thevent to the atmosphere removes exhaled gases to prevent carbon dioxidebuild-up, and hence “rebreathing”, which represent a health risk to themask wearer. Adequate gas washout is achieved by selecting a vent sizeand configuration that allows a minimum safe washout flow at a lowoperating CPAP pressure, which typically can be as low as 4 cm H₂O foradults and 2 cm H₂O for children.

Noise is a significant issue in CPAP treatment for the patient and/orthe patient's bed partner. Excessive noise can lead to patients beingnon-compliant with the CPAP therapy. One source of noise is the exhaustthrough the vent in the mask or conduit. The flow of gas through thevent creates noise as it exits to and interacts with the atmosphere.Noise can adversely affect patient and bed-partner comfort, depending onboth the magnitude and character of the noise. Further, bi-level gasdelivery regimes tend to generate more noise than do constant level gasdelivery regimes. This is thought to be due to the extra turbulencecreated by the gas accelerating and decelerating as it cycles betweenrelatively low and relatively high pressures in the bi-level gasdelivery systems.

The washout vents may offer a generally fixed impedance to air flow (forexample having a generally unchanging geometry with time) or a variableimpedance. In a fixed vent design, the vent flow increases with maskpressure, such that the vent flow may be adequate at a low pressure andexcessive at high pressure. The variations in flow through fixed ventcan lead to noise. Fixed vents are generally simple and inexpensive tomake and operate. A variable vent design could provide a constant ornear constant vent flow across a range of mask pressures having theadvantage that noise will not increase as mask pressure is increased.This may lead to lower vent flow at high pressures which may in turnlead to less noise. However variable vents suffer from difficulties inmanufacture, assembly, consistency, cleaning and usability.

Fixed gas vents are known that have relatively low noise levels, whichlevels may be as low as 30 dBA at a therapy (mask) pressure of 12 cmH₂O. Such vents include, for example, the ResMed MIRAGE™ mask (disclosedin U.S. Pat. No. 6,561,190), the ResMed ULTRA MIRAGE™ mask (disclosed inU.S. Pat. No. 6,691,707), the ResMed VISTA™ mask (disclosed in USPublished Patent application 2003/0196657), the ResMed ACTIVA™ mask thatincludes an elbow with a vent (disclosed in International PatentApplication PCT/AU03/01162 published as WO 2004/022147) and the ResMedMERIDIAN™ disposable nasal mask that includes an elbow incorporating avent (disclosed in International Patent Application PCT/AU2004/000563).The contents of all of these patents and patent applications areincorporated herein by reference in their entireties.

Various quiet vents are known that provide noise levels generally in therange of 25 dBA or less which makes the vent noise difficult todistinguish from transmitted flow generator noise or general backgroundnoise. Examples of quiet vents are disclosed in U.S. Pat. No. 6,581,594and the Weinmann sintered vent. At least the sintered vent is believedto suffer from poor manufacturability, durability, blockage,humidification, sterility/bacterial growth, and/or cleanability.

There is a long felt and continuing need for quiet gas vents for masksand conduits, that are relatively inexpensive, simple in theirconstruction and easy to maintain. Reducing the noise of gas beingexhausted from a mask or conduit can significantly improve the userfriendliness of the CPAP treatment. Providing a simple and easy to uselow-noise vent can reduce the cost of CPAP treatments and thereby assistin making the treatment more affordable to patients suffering from SDB.

SUMMARY OF THE INVENTION

One aspect of the invention is to provide a vent assembly for quietwashout of exhaled gas, which may be accomplished, e.g., using one ormore surface characteristics, such as surface treatment, e.g.,roughening, and/or surface contouring, e.g., scalloped portions that maybe provided to one or more walls of one or more slotted vent apertures.The aperture may take the form of a single arcuate or semi-circular slothaving opposed walls that may subtly converge towards and/or divergefrom one another in the direction of flow. The slot may take the form ofa linear slot and the walls may be parallel to or non-tapering relativeto one another in other embodiments.

In another aspect of the invention, a mask includes a vent assemblyhaving an aperture including one or more of the following features: acurvilinear shape, a slot, converging and/or diverging side walls,surface roughness, scalloping/crenations, a rounded or bell-shapedinlet, a development length and/or exit (or minimal) width designed todevelop appropriate gas washout, and/or material properties (e.g.,density, thickness) to promote quiet exiting of gas.

A particularly preferred embodiment includes a mask with a vent assemblyincluding an aperture including one or more of the following features: acurvilinear shape, a rounded or bell-shaped inlet and/or a developmentlength and/or exit (or minimal) width designed to develop appropriategas washout.

The invention may be embodied as a washout vent for a mask for use witha system for supplying breathable gas pressurized above atmosphericpressure to an airway of a mammal, the washout vent comprising: a ventorifice adapted for gas washout, wherein said orifice at least partiallydefines or completes a conic section, e.g., a circle, ellipse, parabola,hyperbola, etc. In one preferred example, the orifice completes about220°-300°, and preferably 270°, of a circle or an ellipse.

The vent assembly may comprise a single orifice having a shape of ahorse-shoe, ellipse, spiral, curved, straight crescent(s), semi-circle,curvilinear slot portions thereof, or any combination of the above. Theorifice may be a plurality of orifices arranged on the mask or aremovable vent assembly insert. Further, the vent comprises a channelbetween the orifice and the mask shell, wherein the channel has a depthat least as thick as a thickness of the mask and preferably at leastfour times larger than a width of the orifice. The sidewalls of thechannel may converge towards each other and may have a coarse orroughened surface treatment and/or a scalloped surface, to reduce thenoise of the washout gas exhausting through the orifice.

In another embodiment, the invention may comprise a vent assembly forwashout of gas from a mask used with a system for supplying breathablegas pressurized above atmospheric pressure to a human or animal patient,said vent assembly comprising: an orifice in fluid communication with aninterior of the mask, and a solid section at least partially surroundedby the orifice. The vent assembly may be an insert formed from anelastomeric material that is substantially softer and more flexible thanthe hard plastic mask shell, and said insert is selectively andrepeatably attachable to and detachable from the mask. The vent assemblymay be substantially crescent-shaped and includes one or more orificestherethrough. The orifice may have a conic shape e.g., selected from agroup consisting of a horse-shoe, crescent, a 270 degree semi-circle anda curvilinear slot, etc. Further, the vent assembly comprises a channelextending between the orifice and the interior of the mask, and thechannel comprises sidewalls surface treatments, such as a coarse orroughened surface, and the sidewalls may be scalloped.

Another aspect of the invention relates to a washout vent for a mask foruse with a system for supplying breathable gas pressurized aboveatmospheric pressure to an airway of a mammal. The washout vent includesa vent orifice adapted for gas washout. The orifice includes opposededges or side walls. A channel is provided between an orifice exit andan interior surface of the mask. The orifice has a curved configurationincluding a diameter in the range of 4-20 mm extending through an arc inthe range of 130-150 degrees. The channel includes a width in the rangeof 0.5-1.0 mm, a depth in the range of 2.5-3.5 mm, an inlet radius inthe range of 1-2 mm, and a draft angle in the range of 3-7 mm.

Yet another aspect of the invention relates to a mask assembly includinga mask frame and two washout vents provided to the mask frame. Each ofthe vents includes an elongated, curved vent orifice adapted for gaswashout.

Other aspects, features, and advantages of this invention will becomeapparent from the following detailed description when taken inconjunction with the accompanying drawings, which are a part of thisdisclosure and which illustrate, by way of example, principles of thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings facilitate an understanding of the variousembodiments of this invention. In such drawings:

FIGS. 1 and 2 show respectively a front isometric view and rearisometric view of a mask frame incorporating a vent in accordance with afirst embodiment of the invention.

FIGS. 3, 4 and 5 show respectively a front plan view (viewed from themask exterior), a front isometric view and a rear isometric view (viewedfrom mask interior) of the vent shown in FIGS. 1 and 2.

FIGS. 6 and 7 are cross-sectional views of the vent taken along lines6-6 and 7-7 respectively of FIG. 3.

FIGS. 8 to 10 show respectively a front plan view (viewed from maskexterior), a front isometric view and a rear isometric view (viewed frommask interior) of a second embodiment of the vent.

FIGS. 11 and 12 are rear plan and rear isometric enlarged views showinga scalloped surface treatment and crenated outlet edge of the secondembodiment of the vent.

FIG. 11A is a schematic view showing exemplary dimensions and geometryof a vent orifice according to an embodiment of the present invention.

FIGS. 13 and 14 are front plan views of alternative embodiments of thevent.

FIG. 15 is a front view of a vent on an alternative mask.

FIG. 16 is a exploded view of an alternative end cap for the mask shownin FIG. 15.

FIG. 17 is a front isometric view of a swivel elbow with a vent.

FIG. 18 is a front isometric view of the gas conduit shown in FIG. 17without a vent shield.

FIG. 19 is a rear isometric view of the vent shield for the conduitshown in FIG. 17.

FIGS. 20 and 21 illustrate a vent assembly according to yet anotherembodiment of the present invention.

FIG. 22 illustrates a vent assembly according to still anotherembodiment of the present invention.

FIGS. 23-25 illustrate still another embodiment according to the presentinvention.

FIGS. 26 and 27 illustrate yet another vent assembly according to anembodiment of the present invention.

FIGS. 28-34 illustrate additional vent orifices having shapes accordingto embodiments of the present invention.

FIG. 35 is a front plan view of a mask frame including washout ventsaccording to an embodiment of the present invention.

FIG. 36 is a cross-sectional view of a vent a taken along line 36-36 ofFIG. 35 and showing dimensions of an embodiment.

FIG. 37 is an enlarged plan view of a vent taken from FIG. 35 andshowing dimensions of an embodiment.

FIGS. 38-44 illustrate alternative embodiments for orienting two ventson a mask frame.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS 1. First Embodiment ofGas Washout Vent

FIGS. 1 and 2 show a mask frame 10 for use with a system for supplyingbreathable gas pressurized above atmospheric pressure to an airway(s) ofa human or other mammal, e.g., a CPAP or other non-invasive positivepressure delivery system. The mask frame includes a rigid plastic shell12 having an air inlet tube aperture 14 for connection to a supplyconduit to communicate breathable gas from a flow generator (not shown)to the airways of the mask wearer. The mask shell 12 includes a rim 16which supports a flexible sealing membrane (not shown) that provides agas tight seal between the face of the patient and the interior volume17 of the shell 12. The shell 12 includes a support 18 for connectingthe mask 10 to a forehead support (not shown) which includes, e.g., aT-Bar having slotted connectors for receiving headgear straps thatretain the mask over the nose and/or mouth while the patient sleeps. Themask frame may be molded from a generally rigid material such aspolycarbonate.

A vent 20 on the mask includes an orifice 22 for gas washout. Theorifice is partly defined by channel 26 (FIG. 6) that provides a flowpassage from the interior 17 of the mask to the atmosphere. The orificemay in plan view have a conic shape, e.g., opposed walls or edgesdefining the orifice may be formed in any shape that can be defined by acomplete or partial cross-section taken through a cone or a partialconic section. For example, the orifice may be in the form of a circle,hyperbola, ellipse, parabola, semi-circle, or portions thereof. Inaddition, the opposed walls or edges of the orifice may define othershapes, such as a “C”, horse-shoe, crescent, a pair of opposingcrescents, sinusoidal curves, a series of convex and concave segments,spiral, portions or sections thereof, or other curvilinear or evenlinear shapes.

In another sense, the orifice is provided on a solid section 32 of themask that forms a peninsula that is partially surrounded by the orifice.The solid section may be a plate with a bridge to the mask. The solidsection may be in a plane common to the mask and recessed with respectto the orifice or the solid section may be recessed relative to theremainder of the mask such that the vent aperture is flush with theoutside of the mask.

A common characteristic of one embodiment of the curvilinear or linearorifice is that the orifice has a length (L—FIG. 3) substantiallygreater than its characteristic width (W). For example, the length (L)may be at least five (5) times the width (W) of the orifice, and thelength may be preferably 10 to 20 times the width. This ratio may incertain applications be less than five and greater than 20. If theorifice is a plurality of circle segments (or other arrangement ofsegments) the combined length (L) of the segments is substantiallygreater than their average width. Further, the area of the orifice,e.g., length times width (depending on the shape of the orifice), ispreferably about 15 mm² and may be in a range of, for example, 5 mm² to25 mm². The smallest cross-sectional area of the orifice, which mayoccur anywhere along the length of the channel or orifice, defines theresistance of the vent.

As shown in FIGS. 3, 4 and 5, the orifice 22 may be formed at the apexof a raised ridge 24 extending outward from the mask shell or at thebottom of a groove formed in the shell. In the embodiment shown in FIGS.1 to 5, the ridge 24 in plan view is a three-quarters (¾) section of acircle, i.e., it accommodates for and matches the shape of the orifice.

It is thought that an orifice of the configuration shown in FIGS. 3-5helps reduce noise, at least in part, because the jetted air encounters,on exit, air that is not necessarily stagnant, but is moving somewhatdue to neighboring sections of the orifice that promote the movement ofsuch jetted air in the exit direction. Stated differently, the curvednature of the slot, especially one that “folds over” on itself, in theform of a curvilinear section, helps minimize the difference in velocitybetween the jetted air and the surrounding environmental air.

The ridge and/or its orifice may be segmented to form, for example, anarray of circle segments or a pair of opposite crescent ridges. Theorifice, when in the form of a semi-circular shape, defines a peninsula32 that connects to and is formed as part of the mask. The ridge orgroove may have a shape similar but wider than the shape of the orifice.

The diameter (D) (see FIG. 6) of the circle formed by the orifice ispreferably about 6-8 mm, preferably about 6 mm, and may be in a range of4 mm to 20 mm. The diameter (D) of the semi-circular orifice may bedetermined based on the desired surface area, e.g., 15 mm², of theorifice. Further, the diameter (D) may vary beyond the suggested 4 mm to20 mm range depending on the application.

The inner surfaces 28 of the orifice 22 define, or are defined by, achannel 26 extending from the interior 17 of the mask shell to the exitof the orifice 22. The channel 26 may be curvilinear, e.g., horse-shoeshaped, and have a shape similar to the exit of the orifice. In theillustrated embodiment, a gap (W) of the orifice 26 generally narrows(converges) from the mask interior surface to the exit of the orifice.However, the orifice may also diverge in the direction of flow, or theorifice may have a complex shape such that it diverges in one section,and converges in another section of the orifice, in the direction of theflow of gas. In the illustrated embodiment, the gap of the orifice isopen to the interior 17 of the mask shell. The gap between insidesurfaces 28 of the channel walls may be approximately 0.5 mm to 1.0 mm,and preferably 0.75 mm at its narrowest width. The slope of each innersurface may be a draft angle (DA) of 5° from an axis extending throughthe channel. While a draft angle of 5° is preferred, other draft anglesare possible such as angles ranging from 3 to 7 degrees.

The channel 26 may have a depth (DD) approximately four times thenarrowest width of the channel gap (W). The channel depth (DD) is adistance from an inside surface of the mask shell to the exit of theorifice. In a preferred form, the channel depth is 3 mm and the gap (W)is 0.75 mm. The channel depth is generally greater than the thickness(T) of the mask shell, such that the vent and orifice protrude from thesurface of the shell. The mask may have a thickness of 1.0 mm. The ratioof the channel depth (DD) to the width (W) of the orifice is preferably4.0 (e.g., 3.0 mm/0.75 mm), and may be in a range of 2 to 100.

2. Second Embodiment of Gas Washout Vent

FIGS. 8 to 11 show a channel 26 in which the sidewalls 28 have surfacesshaped and/or treated to increase turbulence of air exhausting from thechannel and into the atmosphere. This has the effect of quickly mixingthe vented air with the air from atmosphere, to thereby rapidly reducethe velocity of vented air—which is thought to reduce noise. At least aportion of the interior surfaces 28 of the channel may have a shapedsurface, for example, being scalloped with crenated edges, and/or atreated surface, e.g., a coarse surface treatment such as a roughened orscaled surface. One example of roughening may be in the order of 100-200microns. The surface treatment may be applied to the inner surfaces ofthe channel near the orifice. Scaled refers to a surface treatment thatappears similar to the scales on a fish, such as a shark.

In one embodiment, the surface contouring or shaping may include aseries of scalloped grooves 34, e.g., 10-30 grooves, and preferablyabout 18 grooves in the illustrated example, in each of the interiorsurfaces of the channel as are shown in FIGS. 8 to 12. While the grooves34 are illustrated to have the same dimensions, the size of the groovescould alternate between larger grooves and smaller grooves, or each ofthe grooves could have a different size. Further, at the channel inlet,the side walls may be smooth and not scalloped. As shown in FIGS. 6, 7and 12, the base of the interior walls 28 is well rounded or bell-shapedto facilitate passage of air. Smooth inner surfaces 28 may extend atleast down to one-half the depth of the channel.

Conceptually, the shape of the scalloped grooves may be formed bycutting with cylindrical drill bits that have a diameter wider than theorifice (W) and narrower than the widest portion of the channel.Drilling the sloped channel sidewalls with cylindrical drill bits formsscalloped grooves beginning at the narrow outlet of the channel andextending inward along a portion of the walls. Drilling the grooves alsoyields parabolic edges along the inner walls of the vent. Alternatively,and preferably, the scalloped grooves may be formed during molding byvent molds that include scalloped ridges on the walls of the moldcorresponding to the vent channel. It should be noted that scallopingcan be provided on side walls even if they do not taper, conceptually byusing a conical drill bit and drilling from the exit of the orificeinward.

The outlet edges of the channel, such as surrounding the orifice, may becrenated. The outlet edge 35 of the channel may be a sequence ofrelatively straight segments (S′) and interleaving crenated segments(S), e.g., elliptical or rounded segments. The alternating straight andcrenated segments of the channel edge promote mixing of the jet streamexiting the vent with stagnant air just downstream of the channeloutlet. While the edge segments (S′ and S) are shown as being relativelyuniform, the segments may vary in length and depth along the edge of thechannel. In addition, the width (W′) of the channel is smaller than thewidth (W) of the channel for the scalloped portions to be formed. FIG.11A is a schematic view showing the relative positions of thesedimensions.

3. Third Embodiment of Gas Washout Vent

FIG. 13 is a front plan view of another embodiment of a vent orifice 45having channel sidewalls 44 that have a coarse surface treatment 46 atleast near the edge of the channel at the orifice preferably at the exitedge. The coarse surface is believed to increase the turbulence of airflowing along the sidewalls of the channel. The orifice 45 and theassociated channel (which may be a ridge extending outward from a maskshell 12 or a groove extending into the shell) has a curvilinear shapethat has a serpentine sequence of convex and concave curve segments. Thecoarse surface treatment may be separate from or combined with thescalloped grooves on the channel sidewalls. The interior walls 44 of thechannel may be made coarse 46 by, for example, sandblasting the portionof the mold corresponding to the vent channel.

To mold the vent (either as a separate vent or vent integral with themask) a mold is first formed of the vent, wherein the mold comprises aridge corresponding to a channel and orifice of the assembly. Thegeometry of the mold may be cut to include scalloping features, and thesurface of the mold may be treated, e.g., via sand blasting, to producethe desired level of surface roughness on the interior surfaces of thevent. The surface treatment or contouring is preferably applied to themold sidewalls on opposites sides of the mold section corresponding tothe vent channel and particularly to the exit edge of the vent(orifice). A plastic material (e.g., polycarbonate) is injected into themold to form a molded vent assembly having a channel that possesses thescalloped and/or surface roughness of the mold.

4. Fourth Embodiment of Gas Washout Vent

FIG. 14 is a plan view of alternative orifice 36 and a removableelastomeric insert 40 that fits into an aperture 42 in a mask shell.Vent inserts are known and disclosed in, for example, U.S. Pat. Nos.6,561,190 and 6,561,191 and US Patent Application Publication2003/0079751, each incorporated by reference in its entirety. Whereasvent inserts typically have had an array of small circular orifices, theorifice 36 in FIG. 14 is an extended curvilinear slot. Alternatively, orin addition, the orifice 36 may include a channel as described abovewith a predetermined draft angle, roughening, and/or one or morescalloped portions. The vent insert in FIG. 14 may be identical in itsoutside shape to an existing insert and may fit into existing maskshells. The curvilinear orifice in the replaceable vent 40 allows forcurvilinear slots (such as those shown in this disclosure) to be used onexisting mask assemblies. The insert 42 may be formed of a flexiblepolymer, e.g., Santoprene™ The inserts 42 are removable for replacementand cleaning.

5. Gas Washout Vent On Alternative Mask

FIG. 15 is a perspective view of a mask 50 that includes nozzles 52 thatinterface with the nares of the patient. Similar masks are disclosed in,for example, FIGS. 117 and 130 of US Patent Application Publication No.2004/0226566, which publication is incorporated by reference in itsentirety. Whereas washout vents conventionally have been an array ofcircular openings, the present mask includes one or more curvilinearvents 54 including one or more of the features described above inrelation to FIGS. 3-12, e.g., a slot with converging walls, optionallyprovided with surface contouring or surface treatment, e.g., scallopedportions and/or roughening. The illustrated vent assembly has one ormore elongated orifices that are believed to operate quieter than do theconventional circular vent orifices.

FIG. 16 is a partial exploded view of a yoke, frame, sealing ring andend cap assembly 56 for the mask shown in FIG. 15. The end cap 58 shownin FIG. 16 has a curvilinear washout vent 60. Positioning a single largeorifice vent on the end cap avoids a need for a plurality of vents onanother portion of the mask such as the cushion.

6. Swivel Elbow With Gas Washout Vent

FIGS. 17, 18 and 19 are views of an air inlet conduit 70 that has an airinlet 72 and an air outlet 74, similar to that shown in U.S. Pat. No.6,691,707, the entirety of which is incorporated by reference. A hose(not shown) fits to the inlet to provide pressurized air from a bloweror other source of air. The outlet 74 fits to an aperture in the mask,such as aperture 14 in the mask shown in FIG. 1. An elbow in the conduit70 includes a vent shield 76 that covers at least one vent orifice 78(shown in FIG. 15) which may be a series of curvilinear slot orifices.The orifices exhaust washout gases into a gap between an outer surface80 of the conduit and an inner surface 82 (FIG. 16) of the shield. Acoarse surface treatment 84 may be applied to the inner surface 82 andouter surface 80 in the area corresponding to the gap, especially nearthe outlet to atmosphere. The gap receives washout gas from the vents 78and exhaust the gas at an end 86 of the shield. Scalloped grooves 88 maybe formed on the surfaces 80, 82, such as near the end 86 of the shield.The grooves form crenated edges 90 at the outlet of the gap. These edges90 promote mixing of the washout gas exhausting from the gap withstagnant atmospheric air, which is thought to rapidly decrease thevelocity difference (shear rate) between the atmosphere, reducingexhausted gas and the attendant noise thereof.

FIGS. 20 and 21 illustrate another embodiment of the present inventionwhich is very similar to the embodiment of FIGS. 17-19. However, onlythe cap 76 is provided with surface treatment (e.g., scalloping and/orroughening) on its inside surface.

7. Mask Assembly With Vent Assembly

FIG. 22 illustrates another embodiment of the invention showing a maskassembly adapted to include a vent assembly 200 having one or moresurface treatments (scalloping/roughening) that may be applied to asingle curvilinear aperture 202 provided on the vent cover. More detailsof this mask assembly are disclosed in U.S. patent application Ser. No.10/655,621 filed Sept. 5, 2003, incorporated herein by reference in itsentirety.

8. Alternative Mask Assembly With Vent Assembly

FIGS. 23-25 illustrate a mask assembly including a vent assembly 300according to yet another embodiment of the present invention. Ventassembly 300 is part of a ResMed mask more fully described in U.S. Pat.No. 6,112,746, incorporated herein by reference in its entirety. Themask assembly may include one or more attributes of the vent assemblydescribed in relation to FIGS. 3-12.

9. Alternative Mask Assembly With Vent Assembly

FIGS. 26 and 27 illustrate a portion of a mask assembly 400 as describedin EP 0 985 430 A2, incorporated herein by reference in its entirety.The mask assembly includes a vent assembly 404 to exhaust exhaled gas toatmosphere, e.g., via path 406 defined by an interior wall 408 and anexterior wall 410. Each wall 408, 410 may include one or more surfacetreatments, e.g., scalloping and/or roughening, as described above.

10. Vent Orifice Shapes

FIGS. 28-34 illustrate further orifice shapes according to the presentinvention. In each embodiment, the total open area of the orifice isselected to address adequate gas washout, as described above. FIG. 28 isa ¾ ellipse, as compared to the ¾ circle in FIG. 29. FIG. 30 shows twoparts of an ellipse having areas A1 and A2 which combined form a totalArea (A_(TOTAL)). FIG. 31 shows a generally curvilinear orifice, whileFIG. 32 shows a spiral shaped orifice having multiple component radiiranging from R1 to R2. FIG. 33 illustrates an orifice with curved andstraight sections (delineated by section lines), while FIG. 34 shows an“S”-shaped orifice having radii R1 and R2 that are equal.

11. Mask Frame with Two Curved Washout Vents

FIGS. 35-37 illustrate a mask frame 510 including two curved washoutvents 520 according to an embodiment of the present invention. The vents520 have a generally similar vent structure to the vents 20 describedabove in relation to FIGS. 1-7. However, the two vents 520 are orientedon the mask frame 520 in a particular manner. Also, the vents 520include specific dimensions for an embodiment.

Specifically, each vent 520 includes a diameter of 7.7 mm extendingthrough a 142 degree arc (see FIG. 37). This arrangement improves thestrength of the vent material when compared to a larger arc. As shown inFIG. 36, each vent 520 also has a width of 0.85 mm, a depth of 3 mm, aninlet radius of 1.5 mm, and a draft angle of 6 degrees. Althoughspecific dimensions of the vents 520 are shown in FIGS. 36 and 37, it isto be understood that these dimensions are merely exemplary and otherdimensions are possible depending on application. For example, thediameter may be in the range of 4-20 mm, preferably 6-8 mm, extendingthrough an arc in the range of 130-150 degrees. The width may be in therange of 0.5-1.0 mm, the depth may be in the range of 2.5-3.5 mm, theinlet radius may be in the range of 1-2 mm, and the draft angle may bein the range of 3-7 mm. Also, the vents 520 may include one or moreadditional features as described above, e.g., surface contouring orsurface treatment. Further, the vents 520 may include other orificeshapes such as those described in FIGS. 28-34.

As shown in FIG. 35, two vents 520 are provided to the mask frame 510.As illustrated, the mask frame 510 includes a receiver 562 adapted toreceive a forehead support. The two vents 520 are positioned on the maskframe 510 between spaced-apart side walls 564 of the receiver 562. Inaddition, the two vents 520 are positioned end to end with a small gaptherebetween so that they together define a generally reverse-S shape.Further, the two vents 520 are oriented such that a line L extendingthrough a center of each vent 520 is generally perpendicular to alongitudinal axis A of the mask frame 510.

This vent arrangement on the mask frame 510 allows the width of eachvent 520 to be thinner than if just one vent were used. Also, the twovents 520 may be quieter than one vent, which may be due to the thinnerwidth of each vent and/or more vent perimeter per open area. Inaddition, two vents 520 may reduce the lateral space required on theframe 510. However, it is to be understood that any suitable number ofvents 520 may be provided to the frame 510, e.g., one vent or more thantwo vents. Also, the vents 520 may be oriented on the mask frame 510 inother suitable manners.

FIGS. 38-44 illustrate several alternative embodiments for orienting twovents 520 on the mask frame. For example, the two vents 520 may bevertically aligned with both vents curved downwardly (see FIG. 38) orboth vents curved upwardly (see FIG. 39). The two vents 520 may behorizontally aligned with the vents curved towards one another (see FIG.40) or the vents curved away from one another (see FIG. 41). The twovents 520 may be vertically offset with the vents curved towards oneanother (see FIG. 42). The two vents 520 may be positioned end to endwith a small overlap (see FIG. 43). Also, the two vents 520 may bepositioned end to end with small gap therebetween so that they togetherdefine a generally S shape (see FIG. 44). It is noted that additionalvent configurations may be created by mirroring, rotating, and/orscaling the vent geometry, e.g., see FIGS. 28-34.

While the invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments,it is to be understood that the invention is not to be limited to thedisclosed embodiments, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the invention. For example, while the vent assemblies describedabove may be used in the field of treating patients with sleepdisordered breathing, they may also be beneficial to the field ofrespirators or ventilators in general, e.g., for use in treatment ofother illnesses (e.g., congestive heart failure, diabetes, morbidobesity, stroke, barriatric surgery, etc.), or they may be used in anybreathing apparatus for use with patients or non-patients when ventingin a quiet cost effective manner is desirable.

What is claimed is:
 1. A washout vent for a mask for use with a systemfor supplying breathable gas pressurized above atmospheric pressure toan airway of a mammal, the washout vent comprising: a vent orificeadapted for gas washout, wherein said orifice includes opposed edges orside walls defining at least a portion of a conic section.
 2. A vent asin claim 1 wherein orifice defines a solid section of the vent in theform of a peninsula.
 3. A vent as in claim 1 wherein the vent orificecomprises a semi-circular slot extending approximately 270 degrees.
 4. Avent as in claim 1 wherein the conic section defines a hyperbola,parabola, ellipse, circle, any portion thereof, or any combinationthereof.
 5. A vent as in claim 1 wherein the vent orifice is at an apexof a ridge on the mask.
 6. A vent as in claim 5 wherein the orifice exitis in a plane offset from the mask.
 7. A vent as in claim 6 wherein theorifice exit is in a plane common to the mask.
 8. A vent as in claim 5wherein the ridge is curvilinear in length.
 9. A vent as in claim 1wherein the vent is provided in an insert attachable to the mask.
 10. Avent as in claim 1 wherein the orifice is substantially crescent-shaped.11. A vent as in claim 1 wherein the orifice is one of a plurality oforifices therethrough.
 12. A vent as in claim 1 wherein the orifice hasa horse-shoe shape.
 13. A vent as in claim 1 wherein the orificecomprises convex and concave segments.
 14. A vent as in claim 1 whereinthe orifice comprises a plurality of semi-circular segments.
 15. A ventas in claim 1 wherein the orifice is a partial circle and partiallysurrounds a peninsula portion of the mask.
 16. A vent as in claim 1further comprising a channel between the orifice exit and an interiorsurface of the mask.
 17. A vent as in claim 16 wherein the channel has adepth at least as thick as a thickness of the mask.
 18. A vent as inclaim 16 wherein the channel has a depth at least five times larger thana width of the orifice exit or minimum.
 19. A vent as in claim 16wherein the channel comprises sloping side walls.
 20. A vent as in claim16 wherein the slide walls have a slope of 5 degrees from an axis of thechannel.